code: def split_offset_str(offset_str: str) -> List[str]:
      """Splits a pandas offset string into number part and frequency string part.
  
      Parameters
      ----------
      offset_str : `str`
          An offset string parsable by `pandas`.
          For example, "7D", "-5H", etc.
          The number part should only include numbers and "+" or "-".
          The frequency part should only include letters.
  
      Returns
      -------
      split_strs : `list` [`str`]
          A list of split strings.
          For example, ["7", "D"].
      """
      freq = offset_str.lstrip("+-012334556789")
      num = offset_str[: -len(freq)]
      return [num, freq]
  
imports: import copy
  import dataclasses
  import functools
  import math
  import re
  import warnings
  from dataclasses import field
  from typing import List
  import numpy
  import pandas
  from pandas.testing import assert_frame_equal
  from pandas.testing import assert_index_equal
  from pandas.testing import assert_series_equal
label_desc: Use image node_id 17 for calling a global function with example usage: split_offset_str(offset_str) and returns: list